Plating apparatus and plating method

ABSTRACT

A plating apparatus includes a plating bath configured to perform plating processing of a substrate with a plating solution including an inorganic constituent and an organic constituent introduced into the plating bath, a chemical supplying unit configured to supply each chemical of the inorganic constituent and the organic constituent, an electrode configured to dispose in the plating solution and the electrode configured to selectively adsorb a by-product produced from the organic constituent, and an electric current applying unit configured to apply a predetermined electric current to the electrode.

CROSS-REFERENCE TO RELATED APPLICATION

This application is based upon and claims the benefit of priority from the prior Japanese Patent Application No. 2010-209362 filed on Sep. 17, 2010, the entire contents of which are incorporated herein by reference.

BACKGROUND

Embodiments described herein relate generally to a plating apparatus and a plating method.

In recent years, in manufacturing processes of semiconductor devices, to form a damascene interconnect or the like on a semiconductor substrate, the approach where a wiring trench is formed on the substrate, and a Cu film is deposited within the wiring trench using a plating method has been used.

In such a Cu plating process, a plating solution introduced into a plating bath is so prepared that the plating solution has predetermined concentrations of inorganic and organic constituents. Plate processing is performed in such a manner that substrates are immersed in the plating bath sequentially, and an embedded electroplating current is applied, while the plating solution is circulated.

In this case, since the inorganic and organic constituents in the plating solution are consumed as the plating processing is performed, the replenishment of those constituents is required. The concentrations of the inorganic and organic constituents are regularly measured and monitored using a method such as titration, and based on the result of the measuring and monitoring, the plating solution is replenished with respective chemicals that include the inorganic or organic constituent to keep the respective constituent concentrations in the plating solution equal to the predetermined ones, and some of the plating solution is drained.

While the plating processing is thus performed on the substrates sequentially, besides the original organic constituent of the plating solution introduced at the beginning of the plating processing, by-products dissolved and derived from the organic constituent are produced and accumulated in the plating solution due to the plating processing and the circulation of the plating solution.

The by-products are difficult to detect, and when the Cu film is deposited within the wiring trench, the by-products are adsorbed onto the substrate surface along with the organic constituent and are taken into the Cu film. Therefore, in constant current plating, influences in plating deposition characteristic within the wiring trench, such as the decrease of a bottom-up, the degradation of embedding capability, and the fluctuation of the amounts of impurities, are caused.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a view showing a configuration of a plating apparatus according to an embodiment;

FIG. 2 is a graph showing a relationship between an applied voltage and electric current (a thickness of a film) between electrodes for a leveler and its by-product according to the embodiment;

FIG. 3 is a graph showing a change of a bottom-up relative to the accumulated number of substrates that are plated according to the embodiment;

FIG. 4 is a view showing a configuration of a plating apparatus according to an embodiment;

FIG. 5 is a view showing a configuration of a plating apparatus according to an embodiment; and

FIG. 6 is a schematic view of an adsorbed state of an organic constituent according to the embodiment.

DETAILED DESCRIPTION

Reference will now be made in detail to the present embodiment of the invention, an example of which is illustrated in the accompanying drawings. Wherever possible, the same reference numbers will be used throughout the drawing to refer to the same or like parts.

First Embodiment

FIG. 1 shows a configuration of a plating apparatus according to the present embodiment. As shown in FIG. 1, a plating bath 11 into which a plating solution is introduced and in which plating processing is performed on a substrate 10, a chemical supplying unit 12 that supplies a chemical of each constituent of the plating solution, and a plating solution tank 13 into which chemical is supplied from the chemical supplying unit 12 are provided.

A plating solution circulating line 14 that circulates the plating solution is provided between the plating bath 11 and the plating solution tank 13, and a by-product adsorbing unit 15 is provided along the plating solution circulating line 14.

The plating solution is introduced into the by-product adsorbing unit 15 from the plating solution circulating line 14, and a pair of plate electrodes made up of a negative electrode 16 a and a positive electrode 16 b opposed to the negative electrode 16 a is disposed within the by-product adsorbing unit 15. The negative electrode 16 a and positive electrode 16 b are made up of a material that is insoluble in the plating solution, such as Cu, Pt, and Ti alloy, and are connected to an electric current applying unit 17, such as a power supply.

In such a plating apparatus, the plating processing is performed using a wafer on which a damascene interconnect trench or the like is formed, as the substrate 10.

Each chemical that contains an organic constituent including an accelerator such as a sulfur-based organic compound, a suppressor such as a polyether-based organic compound, and a leveler such as a nitrogen-containing organic compound, or an inorganic constituent such as a cupric sulfate solution, is supplied into the plating solution tank 13 from the chemical supplying unit 12 so that each constituent has a predetermined concentration.

After the supplied plating solution is introduced into the plating bath 11 through the plating solution circulating line 14, the plating processing is performed by sequentially immersing the substrate 10 in the plating bath 11 and applying a predetermined embedded electroplating current. The plating solution is circulated from the plating bath 11 in which the plating processing is performed, to the plating solution tank 13, through the plating solution circulating line 14 and the by-product adsorbing unit 15.

Thus, performing the plating processing on the substrate 10 sequentially while circulating the plating solution, each by-product which is dissolved and derived respectively from the organic constituent, such as the accelerator, the suppressor, and the leveler, is produced in the plating solution. Although some of the by-products are drained together with drainage of the plating solution when the chemicals are replenished as described above, the by-products are accumulated in the plating solution.

When the by-products produced and accumulated in this way, for example, the by-product of the leveler made up of the nitrogen-containing organic compound, exceed a predetermined concentration, a bottom-up is decreased and the embedding is obstructed. Therefore, adsorbing and removing the by-product of the leveler selectively by utilizing the difference in the adsorption characteristic between the leveler added into the plating solution and its by-product, causes the concentration of the by-product of the leveler in the plating solution to be decreased.

In the by-product adsorbing unit 15, therefore, a predetermined electric current is applied between opposed the negative electrode 16 a and positive electrode 16 b by the electric current applying unit 17.

The electric current is applied under the condition that the by-product of the leveler that affects the plating deposition characteristic is selectively adsorbed. FIG. 2 shows a relationship between an applied voltage and electric current (a thickness of a film) between electrodes for a leveler and its by-product. When the applied voltage is changed from a to b, the applied electric current (a thickness of a film) is unchanged for the leveler, while the applied electric current (a thickness of a film) is largely changed for the by-product. That is, by applying the electric current in such a manner that the applied voltage between the negative electrode 16 a and positive electrode 16 b ranges from a to b, the adsorption of the leveler can be suppressed, and the by-product can be selectively adsorbed onto the negative electrode 16 a.

The value of the applied electric current may be slightly lower than the embedded electroplating current that is applied when the plating processing is performed and can be set in the range of 1 to 10 mA/cm² because the molecular weight of the by-product is smaller than that of the leveler. When the value of the applied electric current is less than 1 mA/cm², the adsorption of the by-product is difficult. When the value of the applied electric current exceeds 10 mA/cm², the selective adsorption of the by-product is difficult because the value of the applied electric current is equal to or more than the embedded electroplating current; consequently, the leveler is also adsorbed. The value of the applied electric current is more preferably 2 to 5 mA/cm².

The adsorption removal of the by-product by applying the electric current in the by-product adsorbing unit 15 may be performed continuously or at a predetermined period. The adsorption removal may be performed when, for example, the accumulated number of substrates that are plated or the time period for which plating processing has been performed after supplying the plating solution exceeds a predetermined value. The adsorption removal may be performed when the concentration of the by-product exceeds the concentration that affects plating deposition characteristic.

The adsorbed by-product is not limited to the by-product of the leveler, and any by-products that affect the plating deposition characteristic can be adsorbed and removed in the same way.

The plating processing is thus performed on the substrate 10 sequentially while adsorbing and removing by-products selectively and circulating the plating solution. As is conventionally done, the plating solution is regularly sampled, and the respective concentrations of the inorganic and organic constituents in the plating solution are measured and monitored by a chemical monitoring system using a method such as titration.

The measurement result of the concentrations is fed back to the chemical supplying unit 12, and the plating solution is replenished with the respective chemicals that include the inorganic or organic constituent that is insufficient in the plating solution to keep the respective constituent concentrations in the plating solution equal to the predetermined ones, and some of the plating solution is drained.

Thus, replenishing and draining are repeated. After a predetermined time span, a predetermined accumulated number of substrates that are plated, or a predetermined time period for which plating processing has been performed is accomplished, a new plating solution is prepared.

FIG. 3 is a change of a bottom-up relative to the accumulated number of substrates that are plated according to the present embodiment. As a comparison example, a change of a bottom-up relative to the accumulated number of substrates that are plated when, as is conventionally done, by-products are not removed selectively is also shown in FIG. 3 together. As shown in FIG. 3, although a slight decrease of the bottom-up in the present embodiment can be seen, it is understood that the decrease of the bottom-up in the embodiment is smaller than that of the conventional case because the amount of by-products taken into the plating film surface is suppressed.

According to the present embodiment, since any by-products that affect the plating deposition characteristic can be adsorbed and removed selectively, the stable plating deposition characteristic can be achieved. In particular, when a Cu film is deposited within a wiring trench to form wiring of a semiconductor device, the fluctuation of the bottom-up, the degradation of embedding capability, and the fluctuation of the amounts of impurities can be suppressed and kept constant. Furthermore, since the drainage of active constituents can be suppressed, a plating solution can be efficiently used, which allows a plating solution to be used for a long period of time.

Second Embodiment

Although a plating apparatus similar to the one in the first embodiment is used in the present embodiment, the present embodiment is different from the first embodiment in that the electrode used to adsorb and remove by-products are rotatable.

FIG. 4 shows a configuration of a plating apparatus according to the present embodiment. As shown in FIG. 4, in a by-product adsorbing unit 45, a negative electrode 46 a and a positive electrode 46 b are connected to an electric current applying unit 47 and are connected to a rotation controlling unit 48.

In such a plating apparatus, as with the first embodiment, the plating processing is performed using a wafer on which a damascene interconnect trench or the like is formed, as the substrate 10. As with the first embodiment, in the by-product adsorbing unit 45, a predetermined electric current is applied between opposed the negative electrode 46 a and positive electrode 46 b by the electric current applying unit 47, and by rotating the electrodes by the rotation controlling unit 48, by-products are adsorbed onto the negative electrode 46 a to be removed.

Thus, by-products can be adsorbed easily because rotating the electrode allows the thickness of the reaction layer on the surface of the electrodes to be reduced.

The negative electrode 46 a and positive electrode 46 b both need not necessarily be rotated, and at least the electrode onto which by-products are adsorbed (the negative electrode 46 a in the present embodiment) only needs to be rotatable.

According to the present embodiment, the effect similar to the first embodiment is achieved, and by-products are adsorbed more easily by rotating the electrodes, which allows the removal efficiency of by-products to be improved.

Third Embodiment

Although a plating apparatus similar to the one in the first embodiment is used in the present embodiment, the present embodiment is different from the first embodiment in that the surface of the electrode used to adsorb and remove by-products have a concavo-convex shape.

FIG. 5 shows a configuration of a plating apparatus according to the present embodiment. As shown in FIG. 5, in a by-product adsorbing unit 55, a negative electrode 56 a and a positive electrode 56 b each have a concavo-convex shape on the surfaces of their opposed planes and are connected to an electric current applying unit 57.

In such a plating apparatus, as with the first embodiment, the plating processing is performed using a wafer on which a damascene interconnect trench or the like is formed, as the substrate 10. As with the first embodiment, in the by-product adsorbing unit 55, by applying a predetermined electric current between opposed the negative electrode 56 a and positive electrode 56 b by the electric current applying unit 57, by-products are adsorbed onto the negative electrode 56 a to be removed.

FIG. 6 is a schematic view of an adsorbed state of an organic constituent on the negative electrode 56 a. As shown in FIG. 6, at a concave 61 of the negative electrode 56 b, an accelerator 62 and a suppressor 63 tend to be relatively uniformly adsorbed on the surface of the concave 61, while a leveler 64 is adsorbed more intensively on the shoulder of the concave 61 that is a high electrical field portion, than on any other portion of the surface of the concave 61. Also about by-product, making the surface of the electrode concavo-convex increases the area where local electric field concentration takes place and allows the by-product of the leveler to be more easily adsorbed.

Although a concavo-convex shape preferably has a narrow pitch to form more areas that have high electrical field portions, the concave preferably has, for example, width nearly equal to the width of the wiring that is formed using plating processing. Although the depth of the concave is preferably deeper to adsorb the by-product of the leveler with high selectivity, the concave preferably has, for example, a depth nearly equal to the depth of the wiring that is formed.

The surfaces of both the negative electrode 56 a and the positive electrode 56 b need not necessarily have a concavo-convex shape, and at least the surface of the electrode onto which by-products are adsorbed (the negative electrode 56 a in the present embodiment) only needs to have a concavo-convex shape.

According to the present embodiment, the effect similar to the first embodiment is achieved, and by-products are adsorbed more easily by making the surface of the electrode concavo-convex, which allows the removal efficiency of by-products to be improved.

Furthermore, as with the second embodiment, the electrodes may be rotated, which allows the removal efficiency of by-products to be further improved. In this case, at least the negative electrode 56 a only needs to be rotated.

While certain embodiments have been described, these embodiments have been presented by way of example only, and are not intended to limit the scope of the inventions. Indeed, the novel embodiments described herein may be embodied in a variety of other forms; furthermore, various omission, substitutions and changes in the form of the embodiments described herein may be made without departing from the spirit of the inventions. The accompanying claims and their equivalents are intended to cover such forms or modifications as would fall within the scope and spirit of the inventions. 

What is claimed is:
 1. A plating apparatus, comprising: a plating bath configured to perform plating processing of a substrate with a plating solution including an inorganic constituent and an organic constituent introduced into the plating bath; a chemical supplying unit configured to supply each chemical of the inorganic constituent and the organic constituent; an electrode configured to dispose in the plating solution and the electrode configured to selectively adsorb a by-product produced from the organic constituent; and an electric current applying unit configured to apply a predetermined electric current to the electrodes.
 2. The plating apparatus according to claim 1, further comprising: a plating solution tank into which the chemical is supplied from the chemical supplying unit; a plating solution circulating line provided between the plating bath and the plating solution tank; and a by-product adsorbing unit provided along the plating solution circulating line, the electrodes are disposed in the by-product adsorbing unit.
 3. The plating apparatus according to claim 1, further comprising a rotation controlling unit that rotates the electrode.
 4. The plating apparatus according to claim 1, wherein the electrode have a concavo-convex shape on their surfaces.
 5. The plating apparatus according to claim 1, wherein the electrode is one of a pair of plate electrodes made up of opposed negative and positive electrodes.
 6. The plating apparatus according to claim 5, wherein the negative electrode is rotatable.
 7. The plating apparatus according to claim 5, wherein the negative electrode has a concavo-convex surface.
 8. The plating apparatus according to claim 7, wherein the organic constituent includes an accelerator, a suppressor, and a leveler, and the leveler is a nitrogen-containing organic compound.
 9. The plating apparatus according to claim 1, wherein the electric current applying unit applies the electric current to the electrode continuously or at a predetermined interval.
 10. A plating method, comprising: preparing a plating solution to be predetermined concentrations of an inorganic constituent and an organic constituent in the plating solution respectively; immersing a substrate in the plating solution and performing plating processing; and applying a predetermined electric current to electrode provided in the plating solution and selectively adsorbing the by-product produced from the organic constituent onto the electrode.
 11. The plating method according to claim 10, further comprising circulating the plating solution through a plating solution circulating line, the electrodes are provided along the plating solution circulating line.
 12. The plating method according to claim 10, wherein the organic constituent includes an accelerator, a suppressor, and a leveler, and the by-product of the leveler is selectively adsorbed onto the electrodes.
 13. The plating method according to claim 10, wherein the leveler is a nitrogen-containing organic compound.
 14. The plating method according to claim 10, wherein the predetermined electric current is lower than an embedded electroplating current applied when the plating processing is performed.
 15. The plating method according to claim 10, wherein the predetermined electric current is 1 to 10 mA/cm².
 16. The plating method according to claim 10, wherein the electric current is applied continuously or at a predetermined interval.
 17. The plating method according to claim 10, wherein the electric current is applied while rotating the electrode.
 18. The plating method according to claim 17, wherein the electrode is one of a pair of plate electrodes made up of opposed negative and positive electrodes, and at least the negative electrode is rotated.
 19. The plating method according to claim 10, wherein the electrode has a concavo-convex surface and adsorb the by-product intensively on a shoulder of the concave.
 20. The plating method according to claim 19, wherein the electrode is one of a pair of plate electrodes made up of opposed negative and positive electrodes, and at least the negative electrode has the concavo-convex surface. 